Patent GB-486467-A (GB)
Title: Improvements in or relating to cathode ray oscillographs and like devices
IPC: H01J29/76
Filed: 1937-02-12
Abstract: 486,467. Cathode-ray tubes; electromagnets. PHILCO RADIO & TELEVISION CORPORATION. Feb. 12, 1937, No. 4280. Convention date, Feb. 25, 1936. [Class 39 (i)] [Also in Group XXXV] A cathode-ray tube is provided with first magnetic means for variably deflecting the electron beam in one direction and causing a certain distortion deflection, second magnetic means spaced from the first means along the beam axis for variably deflecting the beam in another direction and causing a certain distortion deflection in such direction as to oppose the first distortion deflection, and means spaced from the first and second means along the axis for variably deflecting the beam in substantially the same direction as the deflection produced by one of the magnetic means. The last deflecting means, which is situated nearest to the cathode of the tube, may be magnetic or electrostatic. The distortions produced are amplitude distortion, i.e. a variation in the displacement of the beam dependent on its position in the field, and direction distortion, i.e. a curvature produced at the edges of the picture, &c., also dependent on the position in the field. Amplitude distortion may be corrected or overcorrected by the use of an electromagnet having concave pole faces or by adding to the field produced by a rectangular yoke the leakage field due to windings on the yoke arms. The vertically-deflecting means may consist of a laminated yoke 8 having windings on the top and bottom arms and laminated extensions 38 ending in polepieces 6. The yoke is arranged round the cathode-ray tube stem and the polepieces 6 extend towards the gun. Between the poles 6 and the yoke 8 is mounted a second laminated yoke 7 having poles 33 carrying windings 34 which produce the horizontal deflections. The yoke 8 may be replaced by a member similar to the yoke 7. The polepieces 6 produce a vertical line deflection of the cathode-ray beam which is deflected horizontally to cover an area by the yoke 7, which at the same time introduces a small amount of amplitude distortion and negligible direction distortion. The yoke 8 then produces the remaining vertical deflection; the field produced by it is corrected so that no amplitude distortion is produced but some direction distortion is produced which serves to correct the amplitude distortion produced by the yoke 7. If any direction distortion of the yoke 7 remains to be corrected this may be done by introducing the requisite amplitude distortion in the field of the yoke 8. By the connection between the polepieces 6 and the yoke 8 the flux due to the former is made proportional to the flux in the yoke but a separate field structure could be used in place of the extensions 38. All the deflecting means may be combined into a single unit by attaching them with bolts to plates 35. Further deflecting means may be arranged between the cathode and the first deflecting means 6, by which distortion may be produced which is balanced out by the subsequent deflecting means. The Specification as open to inspection under Sect, 91 comprises also the use of two magnetic deflecting means only, distortion introduced by one being compensated by distortion introduced by modifying the current producing the deflection by the other deflecting means. This subject-matter does not appear in the Specification as accepted.